Apparatus for sizing pistons



March 3, 1,931. y H, M, RQCKWELL 1,794,797

I APPARATUS FOR SIZING PISTONS Filed April 2l, 1928 4 w Y/ 1% /NL/ENTOR 1f Y 1,/ E L( Patented Mar. 3, 1931 UNITED STATES HUGH M. ROCKWELL,OF FREEPORT, NEW YORK APPABATUS-FR SIZING IPISTONS Application led April 21,

This invention relates to the art of fitting pistons to engine cylinders, and has particular reference to a novel apparatus for accurately sizing the pistons individually.

In order that internal combustion engines and similar power units may operate efficiently. and quietly it is necessary, among other things, to have the pistons well fitted within the cylinders, and for this reason the cylinder bores and piston diameters have had to be very accurately machined and held to close tolerances. The problem is even more aggravated in repair work where, because of scoring or excessive wear, the cylinders have to be rebored and fitted with over-size pistons. As the amount of material bored out under such circumstances may vary according to the degree of wear, it is necessary to carry in stock a. series of different sized pistons, which .20 vary from each other only a few thousandths of an inch. The preesnt invention overcomes these difficulties, and has, as one of its objects, to provide a novel and simplified apparatus for accurately sizing and fitting pistons as desired.

Another object of the invention is to provide such an apparatus by the use of` which the piston may be initially formed to the minimum cylinder size 'and subsequently expanded to the larger required diameter.

A further object is to provide such an apparatus which is equally adaptable for engine manufacturing or assembling plants and for repair shops.

Another object is to provide such an apparatus which will be extremely simple, economical, and a substantial advance in the art.

These and other objects, features, and advantages of the invention will be more read- 40 ily appreciated from the following description in connection with the accompanying drawings, wherein one form of the invention has been shown by way of illustration, and wherein Figure 1 is a vertical longitudinal sectional View through a conventional engine cylinder being fitted with a piston in accordance with the invention Fig. 2 is a similar view illustrating another embodiment of the invention, wherein a 1928. Serial No. 271,726.

standard sizing cylinder is employed for successvely sizing a plurality of pistons;

Fig. 3 is a vertical longitudinal sectional viewthrough one form of piston for the fitting of which the improved apparatus is particularly Well adapted; land F'Fig 4 is a sectional view on line 4.--4 of While the invention is adapted for the manufacture and fitting of various types of pistons, it is particularly suitable for thin steel shell pistons which, because of their lightness in weight, are ada ted for use in airplane, automobile, and ot er high speed engines and the like. The thin skirt makes a quiet piston getting away from piston slap and will not become seized as easily as a ridged piston. I have devised several such pistons, one form of which is shown in Figs. 3 and 4 as comprising a cylindrical body portion 10 of steel or other malleable metal, having at one end, a continuous thin-walled skirt 11, and at its other end an inwardly disposed annular flange 12. Below said fiange 12, the interior of the body portion 10 is counterbored and screw-threaded, as at 13, for the securement of an aluminum head 14 which closes the head end of the piston body 10 and provides wrist pin bosses 15 within the skirt 11. The exterior of the piston body 10 is provided with a plurality of circumferential grooves 16 for the reception of expansion rings of any ordinary or preferred type. In a piston of this type, thev piston skirt will have substantially the same coefficient of expansion as the engine c'ylinder within which it operates, andthus will not be adversely affected by temperature changes, and in view of the thinness `of the skirt portion it will yield readily to conform to the interior of 'the cylinder. the fbore of which may become slightly distorted under the action of heat.

Another form of piston of this general character is disclosed in my Letters Patent No. 1,750,127, issued March 11th, 1930, which differs from the above described form in that the screw threaded connection between the aluminum head and the cast iron body, is at the extremity of the body and in the inner periphery of the annular flange 12. By hav- 'the piston bodies with their skirts are initially formed, preferably by turning in a lathe or the like or by drawing in a press, with an external diameter less than that of the larger cylinder bores. A cylinder 20 of a conventional internal combustion engine is shown in Fig. l, and before fitting the piston therein, the interior of the cylinder is bored or ground accurately to size. The body prtion and its skirt 11 are then centrally disposed within the cylinder bore y and clamped against rotary or longitudinal movement by a suitable clamping device 21, after which the piston skirt is expanded against the wall of cylinder by rolling pressure of an expanding tool 22. The expanding tool 22 is rotatable and is longitudinally movable as it rotates,` with the resultI that it spins the piston skirt, burnishing its inner surface and beneficially compacting the molecular structure of the material. Thus each piston can be conveniently fitted to the particular cylinder in which it is to operate, and in the case of repair work, after a c linder has been rebored, the saine piston can e expanded and used again instead of scrapping the old piston and purchasing a new one.

The specific clamping device 21 shown in the drawings comprises a pair of superimposed discs or plates 23 and 24 of different diameters, the disc 23 being adapted to engage tlie inner periphery of the flange 12, and the disc 24 to engage the interior of the cylinder 20. These discs are'respectively provided with radial slits 25 and 26 whereby to be capable of lateral expansion by a centrally disposed screw 27 and nut A28 as they are I drawn together. The screw 27 has a tapered head 29 seating in a tapered aperture 3() in the disc 23, and the nut 28 is also tapered to snugly fit in a counter sunk aperture 31 in the disc 24. From this it will be seen that the screw 27 and nut 28 not only hold the two discs together, but they expand the discs to frictionally bind the piston flange and the cylinder wall respectively.

After the piston body has thus been clamped within the cylinder 20, the expanding tool 22 is brought into play, as shown, expansively rolling the skirt of the piston against the wall of the cylinder. rIhe expanding tool 22 preferably comprises an arbor 35 having at one end a circular ange or head 36, and at-its other end a tapered key shank 37 by means of which it may be operatively connected in or to a rotary chuck or the like. Intermediate its ends, the arbor 35 is provided with screw threads 38 by means of which lock nuts 39 may be employed to hold a sleeve 40 on the arbor. The inner end of said sleeve 40 is provided with an annular flange 41 adjacent the head 36 and of substantially the same diameter, and the adjacent portions of said flange and head are beveled as indicated at 42 and 43 to define between them an angular or substantially V shaped groove. A circular cage 44 having spaced radial holes 45, encircles said groove and acts as a retainer for an annular series of steel balls 46 or other rolling pressure members. These balls 46 protrude slightly from the periphery of the cage 44 and, in operation, bear directly against the interior of the piston skirt 11 to roll. it against the wall of cylinder 20.

V hen the expanding tool has reached the inner end of the piston skirt 11 it may be withdrawn, and the sizing operation may be finished in one or more strokes of the expanding tool. Then by loosening the screws 27 and nut 28 the discs 23 and 24 will be free to contract, permitting removal of the piston from the cylinder. The aluminum head 14 may then be pinned to the connecting rod, after which the piston. body and skirt are screwedl to said aluminum head, ready for assembling in operating position in the cylinder.

For some purposes such as in quantity production, it may not be either necessary or desirable to fit the pistons'individually to the cylinders in which they are to operate, and therefore .they may be expanded in a special sizing cylinder 50, as shown in Fig. 2. The interior of the cylinder 50 is accurately bored and ground to a definite standard diameter, and preferably the complete apparatus -includes a plurality of such cylinders of different diameters for selective use as desired.

In some instances it may be desirablel to expand the pistons in several successive sta es using cylinders of different diameters xfor ,each stage, and particularly if the piston skirt is annealed, it can be fitted to any one of a series of cylinder sizes. ,The invention is extremely simple, capable of being practiced with economy, and constitutes a substantial advance in the art.

The expanding tool in its simple form, as shown in Fig. 2, is particularly suited for use with a drill press, lathe, or other form of machine tool having a positively guided spindle for driving the arbor. In some instances it may be desirable to operate the expanding tool by a portable hand drill or the like, in which case some suitable form of pilot may be employed to center and guide the arbor. One form of pilot for this purpose is shown in F ig. 1, comprising a cage 'or retainer 50a surrounding the sleeve flange 41 and carrying a plurality of steel balls 51, which are normally urged outwardly by a yeldingly mounted sleeve 52 under the acits longitudinal movement.

Obviously, the invention is susceptible of l numerous modifications` in the details of construction of thel apparatus, and the right is herein-reserved to make such changes as fall within the scope of the appended claims withgut. departing from the spirit of the inven- 1on. 'Having thus desc I claim 1s:-

1. In piston sizing apparatus, means for immovably holding a piston within a cylinder, a rotatable arbor concentric with the cylinder and movable longitudinally in the skirt portion of the piston while so held, and rolling pressure members carried by the inner end of the arbor, said pressure members being rlbed my invention, what vdisposed in a single Plane and adapted to engage the interior o the piston skirt to expand the same against the interior of the cylinder.

2. In piston sizingapparatus, means for immovably holding'a piston within a cylinder, a rotatable arbor concentric with the cylinder and movable longitudinally in the skirt portion of the piston while so held, and an annular series of rolling pressure members carried .by the inner end of the arbor, saidseries of pressure members being disposed in -a single plane and being free rotatable about the axis of the arbor and adapted to enga e the interior of the piston skirt to expand t e same against the interior of the cylinder.

3. In or for piston sizing apparatus, a rotatable arbor having an annular head portion at one end, a bushingy surrounding a portion of said arbor and provided with an annular iange of substantially the same diameter as the head and adjacent theretoz said flange and head portion having their ad] acent edges beveled to define between them a substantiall V shaped circumferential groove, an annu ar series of steel balls adapted to roll in said groove, and a cage retaining said the balls protrude slightly. 4. I nv apparatus of the class described,

' means for clamping a piston within a cylincylinder, and means for holding the two discs together, said means including tapered portions for expanding the discs.

5. In piston sizing apparatus, expansible in a c linder, a rotatable arbor concentric with t e cylinder, and an annular series of steel balls carried by the inner end of said arbor, said steel ,balls being freely rotatable about the axis of the arbor, and being adapted to exert outward radial ressure a ainst the interior of the piston s irt wheriy to expand the same to fit the cylinder.

6. Piston sizing ap aratus comprising in combination, a pair o expansible concentric discs of diierent diameters, one to t within a piston and the other within-a cylinder, tapered means -cooperating to expand said discs res tively against the iston and a ainst t e cylinder whereby to nnmovably c amp the Histon in'the cylinder, an arbor concentrica y-rotatable in the cylmder, said arbor having an annular head portion at one end, a bushing surrounding a portion of said arbor and provided with an annular ange of substantially the same diameter as t e head and adjacent thereto, said flange and head portion having their adjacent edges beveled to deine between them a substantially V shaped circumferential groove, an annular series of steel balls adapted to roll insaid groove, and a cage retaining said steel balls and from the periphery of which the balls protrude slight y.

In testimony whereof, I

signature hereto.l

p HUGH M. ROCKWELL.

have aixed my vsteel balls and from the periphery of which means for clamping a thin-skirt piston with- 

